1. Field of the Invention
The present invention relates to a state monitoring device that monitors the deterioration state of a cutting fluid used when a workpiece is subjected to cutting by a machine tool.
2. Description of the Related Art
Some of machine tools are provided with a cutting-fluid supplying mechanism for carrying out cooling of a tool, removal of chips, lubrication, cleaning upon tool replacement, etc. by spraying a cutting fluid to a cutting region when a workpiece is subjected to cutting. In the cutting-fluid supplying mechanism, the cutting fluid is circulated and repeatedly used. Therefore, impurities such as lubricant oil and microorganisms which cause corrosion are mixed in the cutting fluid, the cutting fluid is deteriorated, and processing is adversely affected as cooling performance reduction, lubrication performance reduction, etc.
As a method for avoiding such adverse effects, Japanese Patent Application Laid-Open No. 2010-188480 (JP 2010-188480 A) describes a monitoring method of monitoring the fluid quality of a cutting fluid, in which a pH sensor, a water-hardness sensor and a concentration sensor are provided to detect the pH value, water hardness and concentration of the cutting fluid, thereby distinguishing the detection values thereof. As a result of that, if the detection values are determined to be within a predetermined normal-value range, a display screen indicative of a normal state is displayed, but if the detection values are determined to be within a caution range, warning is displayed on a display screen, and if the detection values are determined to be in an abnormal range, cutting is prohibited.
Moreover, Japanese Utility Model Publication No. 6-75638 (JP 6-75638 U) describes a cutting-fluid managing device configured to prevent deterioration caused by corrosion of a cutting fluid by pumping up the cutting fluid in a cutting-fluid tank by a pump, heating the cutting fluid by a heater, and killing septic organisms mixed in the cutting fluid, and measure the fluid concentration of the cutting fluid by means of a concentration sensor in order to keep the concentration of the cutting fluid constant by mixing undiluted liquid of the cutting fluid or dilution water in consideration of the measurement result, thereby returning the cutting liquid to the cutting-fluid tank.
When the cutting fluid is deteriorated, cooling performance is reduced and lubrication performance is also reduced, as a result, cutting is adversely affected. Moreover, if the cutting fluid is corroded, all the cutting fluid has to be replaced, and the processes in a factory are temporarily stopped. Furthermore, septic odor is also generated, which leads to deterioration of a working environment.
As a method of detecting deterioration of the cutting fluid, the above-described conventional techniques use the pH sensor, the water-hardness sensor, and the concentration sensor. However, there is a problem that these sensors are affected by the cutting fluid or the impurities mixed in the cutting fluid, the sensor capability is reduced, and it becomes difficult to precisely detect the fluid quality of the cutting fluid.